Les protéines Vestigial-like constituent une famille de cofacteurs de transcription contenant un domaine très conservé, appelé Tondu, qui permet l’interaction avec les facteurs de transcription de la famille TEAD. L’état de l’art des connaissances actuelles sur cette famille, en termes de répertoire, de structure et de fonction des gènes dans les différents groupes d’animaux, a fait l’objet d’une revue. Durant la thèse, a été étudiée la fonction de deux gènes vestigial, vestigial-like 3 et vestigial-like 4, dans le modèle amphibien xénope. Ce choix découle d’une part, des travaux antérieurs de notre laboratoire qui a caractérisé la famille des gènes vestigial chez le xénope et d’autre part des avantages de ce modèle expérimental qui permet les analyses cellulaires et moléculaires. Les approches de gain et perte de fonction indiquent que vestigial-like 3 est plus particulièrement impliqué dans la migration des cellules de la crête neurale. Vestigial-like 4 a un rôle dans la neurogenèse précoce et la formation de la crête neurale. / Vestigial-like proteins belong to a transcription co factors family with a conserved domain, called tondu, which allows their interaction with TEAD family transcription factors. The state of the art on the current knowledge about this family in terms of gene repertory, structure and functions in different animals has given rise to a review. PhD work has focused on vestigial-like 3 and vestigial-like 4 genes functions in the Xenopus amphibian. This choice stemmed from the laboratory previous works that has described vestigial like gene family in Xenopus, and from the Xenopus model advantages that allows cellular and molecular analysis. Gain and loss of function approaches indicate that vestigial-like 3 is especially implicated in neural crest cells migration. Vestigial-like 4 plays a role in early neurogenesis and neural crest formation.

The need to accommodate larger reservoir discharge events has prompted the improvement or replacement of existing spillways. One possible spillway modification is the use of an in-reservoir arced labyrinth weir in place of a linear weir. Arced labyrinth weirs can increase crest length (more cycles) and have improved hydraulic efficiency in non-channelized approach flow applications, compared to traditional labyrinth weir applications. In this study, arced labyrinth weir flow characteristics were observed for eleven different laboratory-scale model geometries at the Utah Water Research Laboratory. Rating (Cd vs. HT/P) data and observations were recorded for each configuration, and discharge efficiency was determined. Cycle efficiency, which is representative of the discharge per cycle, was also reported.

No description available.

The vertebrate nervous system is extremely complex and contains a wide diversity of cell types. The formation of a functional nervous system requires the differential specification of progenitor cells at the right time and place. The generation of many different types of neurons along the rostro-caudal axis of the CNS begins with the initial specification of a few progenitor domains. This initial coarse pattern is refined by so-called secondary organizers arising at boundaries between these domains. The Isthmic Organizer (IsO) is a secondary organizer located at the boundary between the midbrain and the hindbrain. Although the function and maintenance of the IsO are well understood, the processes underlying its initial specification have remained elusive. In the present work we provide evidence that convergent Wnt and FGF signals initiate the specification of the IsO during late gastrulation as part of the neural caudalization process. The initial step in the generation of the nervous system is the division of the embryonic ectoderm into three cell populations: neural cells giving rise to the CNS, neural plate border cells giving rise to the peripheral nervous system, and epidermal cells giving rise to the outer layer of the skin. While the choice between neural and epidermal fate has been well studied, the mechanism by which neural plate border cells are generated is less well understood. At rostral levels of the neuraxis, the neural plate border gives rise to the olfactory and lens placodes, thickenings of the surface ectoderm from which sensory organs are derived. More caudally, the neural plate border generates neural crest cells, a transient population that migrates extensively and contributes to neurons and glia of the peripheral nervous system. How the early patterning of the central and peripheral nervous systems are coordinated has remained poorly understood. Here we show that the generation of neural plate border cells is initiated at the late blastula stage and involves two phases. During the first phase, neural plate border cells are exposed to Wnt signals in the absence of BMP signals. Simultaneous exposure to Wnt and BMP signals at this early stage leads to epidermal induction. Wnt signals induce expression of Bmp4, thereby regulating the sequential exposure of cells to Wnt and BMP signals. During the second phase, at the late gastrula stage, BMP signals play an instructive role to specify neural plate border cells of either placodal or neural crest character depending on the status of Wnt signaling. At this stage, Wnt signals promote caudal character simultaneously in the neural plate border and in the neural ectoderm. Thus, the choice between epidermal and neural plate border specification is mediated by an interplay of Wnt and BMP signals that represents a novel mechanism involving temporal control of BMP activity by Wnt signals. Moreover, the early development of the central and peripheral nervous systems are coordinated by simultaneous caudalization by Wnt signals.

<p>The two major contributing populations to the outflow tract of the heart are the secondary heart field and the cardiac neural crest. These two populations are responsible for providing the myocardium that supports the outflow tract valves, the smooth muscle that surrounds these valves and the outflow vessels themselves, and the septum that divides the primitive, single outflow tract into an aorta and pulmonary trunk. Because the morphogenesis of this region is so complex, its development is regulated by many different signaling pathways. One of these pathways is the Sonic hedgehog pathway. This thesis tests the hypothesis that Sonic hedgehog induces secondary heart field proliferation, which is necessary for normal outflow tract development. To address this hypothesis, I took advantage of small chemical antagonists and agonists to determine how too little or too much hedgehog signaling would affect the secondary heart field, both in in vitro explants and in vivo. I have determined that Sonic hedgehog signaling maintains proliferation in a subset of secondary heart field cells. This proliferation is essential for generating enough myocardium and smooth muscle and also for the cardiac neural crest to septate the outflow tract into two equal-sized vessels. Up-regulating hedgehog signaling induces proliferation, which is quickly down-regulated, showing that the embryo exhibits a great deal of plasticity. Together, these studies have shown that Sonic hedgehog promotes proliferation in a subset of the secondary heart field and that the level of proliferation must be tightly regulated in order to form a normal outflow tract.</p> / Dissertation

The real phenomena of sea surface are interacting by much kind of different waves.In these phenomena, the gravity standing wave is most important. The gravity standing wave is formed by two progressive waves that possessing same properties but opposite directions. Gravity standing wave can also form by the interaction of a progressive wave with it¡¦s totally reflection wave. Because of the nonlinear interaction of two waves, there must result a double-crest phenomenon of wave pressure. It is dangerous for the navigation of ship when the double-crest appears, and it¡¦s certainly to take the phenomenon into consideration when we are going to design a jetty. In this paper, it bases on the reference of Chen (1989, 1990) who obtained a third-order approximation of two-wave trains interactions in a uniform depth wave field. Further, in this paper, it checks the result that the double-crest phenomenon is formed by which one of these nonlinear terms. Furthermore, research the influences of wave steepness, wave periods, and water depths these factors will cause the crest diverges is also the purpose.

Τα κύτταρα της νευρικής ακρολοφίας είναι ένας πολυδύναμος πληθυσμός βλαστικών κυττάρων που δημιουργείται στη ραχιαία πλευρά του νευρικού σωλήνα των σπονδυλωτών κατά τη διάρκεια της νευριδίωσης. Μετά τη δημιουργία τους, τα κύτταρα της νευρικής ακρολοφίας μεταναστεύουν σε ολόκληρο το έμβρυο, ακολουθώντας συγκεκριμένα μονοπάτια, συνεισφέροντας στη δημιουργία μιας μεγάλης ποικιλίας δομών, όπως νευρικά και γλοιακά κύτταρα του περιφερικού νευρικού συστήματος (ΠΝΣ), μελανοκύττρα, δομές που συμβάλλουν στο σκελετό του κρανίου και του προσώπου κλπ. Η δημιουργία, η αυτο- ανανέωση και η διαφοροποίηση των κυττάρων της νευρικής ακρολοφίας απαιτούν το συντονισμό των διεργασιών του κυτταρικού πολλαπλασιασμού και της κυτταρικής διαφοροποίησης. Η αδυναμία συντονισμού των παραπάνω διαδικασιών οδηγεί στην εμφάνιση ασθενειών στον άνθρωπο (neurocristopathies). Η Geminin είναι ένα μόριο που έχει την ικανότητα να ρυθμίζει την πρόοδο του κυτταρικού κύκλου, αλληλεπιδρώντας με τον παράγοντα αδειοδότησης της αντιγραφής Cdt1, και τη διαφοροποίηση, μέσω της αλληλεπίδρασής της με μεταγραφικούς παράγοντες και πρωτεΐνες αναδιαμόρφωσης της χρωματίνης. Προηγούμενες μελέτες του εργαστηρίου μας έχουν αναδείξει τη Geminin ως ένα σημαντικό ρυθμιστή των διαδικασιών της αυτο- ανανέωσης και διαφοροποίησης στα πρόδρομα νευρικά κύτταρα στον αναπτυσσόμενο φλοιό. Προκειμένου να κατανοήσουμε τους μηχανισμούς που ελέγχουν την αυτο-ανανέωση και τη διαφοροποίηση των πολυδύναμων κυττάρων της νευρικής ακρολοφίας και να κατανοήσουμε το μοριακό μηχανισμό ασθενειών στον άνθρωπο που σχετίζονται με την απορρύθμιση του ελέγχου της ι κανότητας αυτο-ανανέωσης και διαφοροποίησης των πολυδύναμων κυττάρων της νευρικής ακρολοφίας μελετήσαμε το ρόλο της Geminin στη δημιουργία, την αυτο-ανανέωση, τον καθορισμό και τη διαφοροποίηση των κυττάρων της νευρικής ακρολοφίας. Προς αυτή την κατεύθυνση πραγματοποιήθηκαν τόσο in vivo όσο και in vitro πειράματα, χρησιμοποιώντας ζωικά μοντέλα τα οποία δημιουργήθηκαν από το εργαστήριο μας και στα οποία το γονίδιο της Geminin είχε αδρανοποιηθεί ειδικά στα κύτταρα της νευρικής ακρολοφίας. Τα αποτελέσματά μας έδειξαν ότι η απουσία της Geminin οδηγεί στη δημιουργία εμβρύων με σοβαρές μορφολογικές αλλοιώσεις, που κατά τα πρώιμα αναπτυξιακά στάδια χαρακτηρίζονται από την απουσία της δομής του μεσεγκεφάλου και των βραγχιακών τόξων και σε μεταγενέστερα αναπτυξιακά στάδια εμφανίζουν σοβαρή κρανιοπροσωπική δυσμορφία, με κατάληξη το θάνατο των εμβρύων, λίγες ημέρες πριν γεννηθούν. Επιπλέον, κατά τα πρώιμα αναπτυξιακά στάδια παρατηρήθηκαν σοβαρές αλλοιώσεις σε δομές που προέρχονται από τη νευρική ακρολοφία, όπως είναι τα κρανιακά και τα ραχιαία γάγγλια, οι γναθικές προεκβολές και τα πρόδρομα κύτταρα του εντερικού νευρικού συστήματος. Η μείωση του πληθυσμού των πρόδρομων κυττάρων του εντερικού νευρικού συστήματος (ΕΝΣ) οδήγησε στη δημιουργία ενός αγαγγλιονικού εντέρου, το οποίο παρομοιάζει με το φαινότυπο του ΕΝΣ στη νόσο Hirschsprung στον άνθρωπο. Η ιστοειδική αδρανοποίηση της Geminin οδήγησε στη μείωση των αδιαφοροποίητων κυττάρων νευρικής ακρολοφίας που δημιουργούνται στην αυχενική περιοχή του νευρικού σωλήνα και στην είσοδο μικρότερου αριθμού κυττάρων νευρικής ακρολοφίας στον γαστρεντερικό σωλήνα κατά τα πρώτα στάδια του αποικισμού του. Μελέτη των εντερικών κυττάρων νευρικής ακρολοφίας έδειξε ότι η αποσιώπηση της Geminin προκάλεσε την αύξηση της απόπτωσης κατά τις ηλικίες Ε9.5 και Ε10.5 και τη μείωση του κυτταρικού πολλαπλασιασμού τους κατά την ηλικία Ε9.5. Σε συνδυασμό με τη μειωμένη ικανότητα που δείχνουν τα πρόδρομα εντερικά κύτταρα να αυτο-ανανεώνονται, τα αποτελέσματά μας προτείνουν ότι η Geminin έχει σημαντικό ρόλο στην αυτο-ανανέωση και την επιβίωση των πρόδρομων κυττάρων του ΕΝΣ. Επιπλέον, η απουσία της Geminin οδηγεί στη μείωση των κυττάρων που έχουν καθορισμένη μοίρα και εκφράζουν τους δείκτες των πρόδρομων εντερικών κυττάρων Phox2b, Ret και Mash1, ενώ τα κύτταρα αυτά απουσία της Geminin παρουσιάζουν μειωμένη παραγωγή νευρικών κυττάρων, κατά την έναρξη της νευρωνικής διαφοροποίησης. Συμπερασματικά, τα αποτελέσματά μας αναδεικνύουν τη Geminin ως ένα σημαντικό μόριο κατά τη δημιουργία των πολυδύναμων κυττάρων της νευρικής ακρολοφίας. Επίσης η Geminin είναι απαραίτητη για τη δημιουργία των κυττάρων της νευρικής ακρολοφίας που αποικίζουν το γαστρεντερικό σωλήνα, ενώ ρυθμίζει την επιβίωση και την αυτο-ανανέωσή τους, καθώς και τη μετάβασή τους από την αρχικά αδιαφοροποίητη/πολυδύναμη κατάσταση στην εντερική αναπτυξιακή μοίρα. Επιπλέον η απουσία της Geminin δημιουργεί μύες οι οποίοι μιμούνται τη νόσο του Hirschsprung και αποτελούν ένα σημαντικό ζωικό μοντέλο για τη μελέτη των μηχανισμών της μοριακή παθογένειας της νόσου αλλά και στην εύρεση νέων θεραπειών. / The neural crest is a multipotent cell population that is formed at the dorsal neural tube of vertebrate embryos during neurulation. After their formation, neural crest cells (NCCs) delaminate from the neural tube and migrate throughout the embryo following specific pathways, and give rise to a wide variety of structures, such as neural and glial cells of the peripheral nervous system (PNS), melanocytes, structures of the craniofacial skeleton, etc. Neural crest formation, self-renewal and differentiation require the coordination of proliferation and differentiation. Deregulation of these processes results in developmental diseases in humans, known as neurocristopathies. Geminin is a molecule that has the ability to regulate cell cycle progression and differentiation, through interactions with the licensing factor Cdt1, transcription factors and chromatin remodeling factors. Previous studies from our laboratory have shown that Geminin is an important regulator of self-renewal and differentiation of early cortical progenitors. In order to understand the mechanisms that control self-renewal and differentiation of multipotent neural crest cells (NCCs) and gain insight into the molecular mechanism of human diseases, we studied the role of Geminin in the formation, self-renewal and differentiation of NCCs. Towards this direction, we performed in vivo and in vitro experiments, using animal models that have been generated in our laboratory and allow the conditional inactivation of Geminin in neural crest cells. Our results showed that deletion of Geminin causes severe morphological malformations in embryos that are characterized by the absence of midbrain, branchial arches and severe craniofacial malformation. Mutant embryos are dying a few days before birth. Moreover, during early embryonic development, the neural crest-derived structures, such as cranial and dorsal root ganglia, the maxillary and the mandibular components, and enteric progenitor cells, were severely affected. The decrease of enteric neural crest cells resulted in the formation of aganglionic gut that resembles with the phenotype of Hirschsprung disease. The conditional inactivation of Geminin resulted in the decreased formation of naïve vagal neural crest cells, while enteric neural crest cells were dramatically reduced. Geminin deficient enteric neural crest sells show increased apoptosis at E9.5 and E10.5, and decreased cell proliferation at E9.5. These findings, combined with the decreased self-renewal capacity of enteric progenitor cells (EPCs) in vitro, suggest that Geminin is important for the self-renewal and the survival of ENS progenitor cells. In addition, deletion of Geminin resulted in decreased committed enteric neural crest cells, that express enteric progenitor markers Phox2b, Ret and Mash1. In conclusion, our results highlight Geminin as an important molecule during the formation of multipotent neural crest cells. Geminin is required for the formation of vagal neural crest cells that colonize the gastrointestinal tract, and regulates survival and selfrenewal of these cells, as well as their transition from a multipotent state to the committed enteric lineage of progenitor cells. Moreover, conditional inactivation of Geminin leads to Hirschsprung-like phenotype that could be used as model organisms to study disease pathogenesis and help in the discovery of new therapies.

Dental caries and periodontal disease are the major causes for tooth loss. While dental caries commonly involve the posterior teeth in both jaws, the teeth most commonly lost due to periodontal problems are the first and second molars in the maxilla. As a consequence, the upper posterior jaw is frequently edentulous. Implant therapy today is a predictable treatment modality for prosthetic reconstruction of edentulous patient. Insufficient amounts of bone, due to atrophy following loss of teeth or due to the presence of the maxillary sinus, can make it impossible to insert implants in the posterior maxilla. During the 1970s and 1980s, Tatum, Boyne and James and Wood and Moore first described maxillary sinus floor augmentation whereby, after the creation of a lateral access point, autologous bone grafts are inserted to increase crestal bone height and to create the necessary conditions for the insertion of implants. This surgical procedure requires a two-stage approach and a double surgical site: first, bone is harvested from a donor site and transplanted to the recipient site; then, after a proper healing period of between 4 to 6 months, the implants are inserted. This kind of bone reconstruction, even if well documented, has its limitations, not least in the creation of two different surgical sites and the consequent increased risk of morbidity. In 2004, Lundgren et al. described a new, simplified technique for the elevation of the sinus floor. The authors showed that by lifting the sinus membrane an empty space was created in which blood clot formations resulted in the establishment of new bone. The implants were placed simultaneously to function as “tent poles”, thus maintaining the sinus membrane in a raised position during the subsequent healing period. An essential prerequisite of this technique is to obtain optimal primary implant stability from the residual bone in the sinus floor. An extremely resorbed maxillary sinus floor, with, for example, less than 2-3 mm of poor quality residual bone, could impair implant insertion. The aims of the present research project were (i) to evaluate the donor site morbidity and the acceptance level of patients when a bone graft is harvested from the anterior iliac crest, (ii) to evaluate implant stability, new bone formation inside the maxillary sinus and marginal bone resorption around the implants in long term follow up when maxillary sinus floor augmentation is performed through sinus membrane elevation and without the addition of any grafting material, (iii) to investigate new bone formation inside the maxillary sinus, in experimental design, using a resorbable space-maker device in order to maintain elevation of the sinus membrane where there is too little bone to insert implants with good primary stability. In Paper I, 70 consecutively treated patients were retrospectively evaluated in terms of postoperative donor site morbidity and donor site complications. With regard to donor site morbidity, 74% of patients were free of pain within 3 weeks, whereas 26% had a prolonged period of pain lasting from a few weeks to several months. For 11% of patients there was still some pain or discomfort 2 years after the grafting surgery. Nevertheless, patients acceptance was high and treatment significantly improved oral function, facial appearance, and recreation/social activities and resulted in an overall improvement in the quality of life of formerly edentulous patients. In Paper I and III, some differently shaped space-making devices were tested on primates (tufted capuchin - Cebus apella) in two experimental models aimed at evaluating whether a two-stage procedure for sinus floor augmentation could benefit from the use of a space-making device to increase the bone volume and enable later implant installation with good primary stability, without the use of any grafting material. An histological examination of the specimens showed that it is possible to obtain bone formation in contact with both the Schneiderian membrane and the device. In most cases the device was displaced. The process of bone formation indicated that this technique is potentially useful for two-stage sinus floor augmentation. The lack of device stability within the sinus requires further improvement in space-makers if predictable bone augmentation is to be achieved. In Paper IV, a total of 84 patients were subjected to 96 membrane elevation procedures and the simultaneous placement of 239 implants. Changes of intra-sinus and marginal bone height in relation to the implants were measured in intraoral radiographs carried out during insertion after 6 months of healing, after 6 months of loading and then annually. Computerised tomography was performed pre-surgically and 6 months post-surgically. Resonance frequency analysis measurements were performed at the time of implant placement, at abutment connection and after 6 months of loading. The implant follow-up period ranged from a minimum of one to a maximum of 6 years after implant loading. All implants were stable after 6 months of healing. A total of three implants were lost during the follow-up period giving a survival rate of 98.7%. Radiography demonstrated an average of 5.3 ± 2.1 mm of intra-sinus new bone formation after 6 months of healing. RFA measurements showed adequate primary stability (implant stability quotient 67.4 ± 6.1) and small changes over time. In conclusion, harvesting bone from the iliac crest could result in temporary donor site morbidity, but in 11% of patients pain or discomfort was still present up to 2 years after surgery. However, patient satisfaction was good despite this slow or incomplete recovery, as showed by the quality of life questionnaire. Maxillary sinus membrane elevation without the use of bone grafts or bone substitutes results in predictable bone formation both in animal design, where the sinus membrane is supported by a resorbable device, and in clinical conditions, where the membrane is kept in the upper position by dental implants. This new bone formation is accompanied by a high implant survival rate of 98.7% over a follow-up period of up to 6 years. Intra-sinus bone formation remained stable in the long-term follow-up. It is suggested that the secluded compartment allowed bone formation in accordance with the principle of guided tissue regeneration. This technique reduces the risks of morbidity related to bone graft harvesting and eliminates the costs of grafting materials.

No description available.

The neural crest (NC) derives from the dorsal borders of the vertebrate neural tube. During development, the NC cells migrate and contribute to the formation of different tissues and organs. Along the anteroposterior axis, the NC gives rise to neurons and glia of the peripheral nervous system and to melanocytes. Furthermore, the cephalic NC yields mesenchymal tissues, which form all facial cartilages and bones, the large part of skull, facial dermis, fat cells and smooth muscle cells in the head. In the trunk of amniotes Vertebrates, these tissues are derived from the mesoderm, not from the NC. In lower Vertebrates, however, the trunk NC generates some mesenchymal tissues, such as in the dorsal fins of zebrafish. The question therefore is raised whether the ability of the NC to produce mesenchymal cells was totally lost in the trunk of amniote Vertebrates during evolution, or if it can still be achieved under specific conditions. This work is interested in uncovering the mesenchymal potential of the avian trunk NC, with special interest in the differentiation into osteoblasts and adipocytes.Our experimental approach was to examine the skeletogenic and adipogenic differentiation potentials of quail trunk NC cells after in vitro culture. Cell differentiation was evidenced by the analysis of lineage-specific genes and markers using in situ hybridization (ISH), immunocytochemistry and RT-PCR. The established culture conditions allowed observation of both skeletogenesis and adipogenesis. Osteogenesis was initially characterized by expression of Runx2, the first transcription factor specific of the osteoprogenitors, which was detected by ISH from 5 days of culture. Later, we observed osteoblast maturation, with the expression of collagen1 protein, osteopontin mRNA and alkaline phosphatase mRNA, until the bone matrix mineralization stage. The trunk NC cells also underwent chondrogenesis, as demonstrated by Sox9, aggrecan and collagen10 mRNA expression, and Alcian blue staining. The observation of the mineralized areas and chondrogenesis suggested that the trunk NC cells in vitro are able to perform endochondral and membranous ossifications. In same culture conditions, the cells differentiated also into adipocytes, identified from 10 days of culture by Oil Red O staining. The mRNAs of the CEBP, PPAR and FABP4 adipogenic markers were detected by RT-PCR from 3 days of culture. For the characterization of bone and adipocyte progenitors, we evaluated the differentiation potential of individual trunk NC cells. The phenotypic analysis of these clonal cultures showed that 76% of the cells generated Runx2-positive osteoblasts. Moreover, most of the clone-forming trunk NC cells were multipotent progenitors endowed with both neural and osteogenic potentials. Furthermore, in another clonal culture condition, adipocytes were found in 35.3% of the clones, and approximately half of them also contained glial and/or melanogenic cells.These results show that the trunk NC cells in vitro are able to differentiate not only in their classical derivatives found in vivo (melanocytes, neurons and glial cells), but also in mesenchymal phenotypes, including adipocytes and osteoblasts. Importantly, as in cephalic NC cells, mesenchymal phenotypes differentiated from multipotent progenitor cells, suggesting that, during evolution, the NC stem cells intended for both mesenchymal and neural fates, had the expression of their mesenchymal potential inhibited in the trunk. Thus, although at the dormant state and not expressed in vivo, a significant mesenchymal potential is present in the trunk NC cells of amniotes Vertebrates and can be disclosed in vitro